This morning we get new information that is allowing us to retrace the footsteps of Carl Pearson. The high school senior opened fire inside -- school on Friday he had an arsenal that included a shotgun Molotov cocktails and even a machete. His attack was bloody and quickly over in little more than a minute so let's go -- -- ABC's ladies and -- -- in Centennial, Colorado Clayton. Good morning did take a look at this you can see some of the backpacks and cell phones that were left behind hundreds of them -- students lead in the chaos on Friday. And this morning school officials are reviewing video camera footage from inside showing the speed and violence of this attack. Investigators say at 12:30 PM senior Carl -- parks his car and walks in the north side of the building. Carrying a twelve gauge shotgun. Extra ammunition slung across his chest. He was also armed with a machete. Very large. Night. The individual also period backpack with him as he entered the school. Pearson police say began shooting immediately once down a hallway then aiming for -- Davis just seventeen. Firing at point blank range. She was an innocent victim. Of an evil act of violence. After shooting Davis -- goes to the library firing again then lighting one of three Molotov cocktails he carries in a backpack. -- library. Come to the -- As the campus scrambles to lockdown the schools deputy sheriff and an unarmed security officer -- of the library toward the sound of gunfire. Pearson police say knows they are closing in. Individual fired. And then ran into the back corner which would be the north edge of the library. And there took his own life. This morning -- Davis is in critical condition fighting for a life changed in a moment. That happened lightning fast knowledge her -- hope she's doing good. This -- not want to finance from beginning to end the entire nightmare just eighty seconds. -- I started a stopwatch at the beginning of our story it ran ninety seconds that is ten seconds longer than this entire incident ran from beginning to end. Over so quick but the impacts lasting a lifetime beyond.

This transcript has been automatically generated and may not be 100% accurate.

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